JP5713512B2 - Dislocation engineering in single crystal synthetic diamond materials - Google Patents

Description

  The present invention relates to a method of producing a single crystal diamond material by chemical vapor deposition (CVD) technology. Certain embodiments relate to methods that allow control of the number, distribution, direction, and / or type of dislocations in a single crystal CVD diamond material. Certain embodiments also relate to single crystal diamond materials that can be manufactured according to the methods described herein. Certain embodiments of the present invention also relate to the use of these materials in optical devices, mechanical devices, luminescent devices and / or electronic devices.

Dislocations significantly and often undesirably affect the physical and electro-optical (photoelectron) properties of crystalline diamond solids. For example, toughness and / or wear resistance may be affected by dislocation density and dislocation direction. In addition, dislocations can adversely affect the performance of optical or electronic devices that utilize crystalline diamond materials.
Diamond is a material that is famous for its exceptional hardness and mechanical properties, and as a result, diamond is used in several applications (eg, drilling). Dislocations are known to adversely affect these properties, particularly homoepitaxial CVD synthetic diamond materials, and dislocations typically propagate in a direction that is generally parallel to the growth direction of the material. The resulting parallel array of dislocations is likely to adversely affect the mechanical properties of the material.

  As a result of significant density of parallel dislocations, for example, parallel dislocations propagated in the <001> direction of synthetic diamond crystals homoepitaxially grown on a (001) substrate, considerable strain is created in the synthetic diamond material, thus resulting in birefringence, This has been found to reduce its performance for certain optical applications such as Raman lasers (for example, see Walter Lubeigt et al., “An Intra-Cavity See “An intra-cavity Raman laser using synthetic single-crystal diamond”, Optics Express, 2010, Vol. 18, No. 16. I want to be) Therefore, it is desirable to reduce the total strain in the material or at least achieve a good strain distribution in order to provide good optical performance. High birefringence is observed when the optical observation axis is in the same direction as the parallel dislocation line direction, ie, parallel to the growth direction. In optical applications, for simple engineering considerations (eg, area maximization), it is conventional practice to process the material with respect to the major plane perpendicular to the growth direction. This results in dislocations perpendicular to the major surface of the material and parallel to the viewing axis, resulting in high birefringence.

  Also, different dislocation types and directions can adversely affect the performance of CVD synthetic diamond devices. The ability to select a particular line direction of dislocations (more precisely, “the line direction of dislocations”) can affect the optical and / or electronic properties of diamond-based devices. It is assumed that it can be optimized for the specific application desired.

  In light of the foregoing, one problem to be solved is to mitigate the adverse effects of certain dislocation types and / or orientations of single crystal CVD synthetic diamond materials, especially for optical, mechanical, luminescent and electrical applications. There is to do.

The above problems have been solved, at least in part, in the past by developing methods that reduce the number of dislocations in order to minimize the undesirable effects of dislocations. For example, WO 2004/027123 and 2007/066215 form CVD synthetic diamond materials with low dislocation concentrations to provide high quality optical, electronic and / or detector grade diamond materials. A method is disclosed. However, it can be said that forming a CVD synthetic diamond material having a low dislocation density is relatively difficult, time consuming and costly.

表１：（００１）成長後の垂直方向にスライシングされた一次ＣＶＤ層上の［００１］成長は、二次層の貫通転位が［０１０］線方向である場合に種々の転位タイプを示す。 Although there are other dislocation sources, the two main dislocation sources are (i) threading dislocations from the substrate to the CVD layer and (ii) dislocations occurring at the interface between the substrate and the CVD layer. Can be mentioned. With regard to (i), slicing the primary CVD layer vertically to expose the (001) plane and growing a secondary layer on the (001) plane results in the primary layer to the secondary layer. Threading dislocations occur (in this case, the Burgers vector is preserved). Assuming that the dislocations in the primary layer are in the <001> direction and are of the edged 45 ° mixed type, there are many permutations of threading dislocations in the secondary CVD layer (see Table 1). . However, all threading dislocations are in the <100> direction and are either blade type or 45 ° mixed type. Thus, this work demonstrates some degree of dislocation engineering, but this is limited in both dislocation line direction and dislocation type. Previous studies on (ii) (eg MP Gaukroger et al., "Diamond and Related Materials", Vol. 17, 2008) (See pages 262-269), substrate pretreatment has the role of determining the dislocation type in the CVD layer grown on a standard (001) substrate. Dislocations propagating from surface defects (eg, roughly polished substrates) are generally of the 45 ° mixed type, ie the most stable dislocation type during (001) growth.

Table 1: [001] growth on vertically sliced primary CVD layer after (001) growth shows various dislocation types when the secondary layer threading dislocations are in the [010] line direction.

International Publication No. 2004/027123 Pamphlet International Publication No. 2007/066215 Pamphlet

Walter Lubeigt et al., “An intra-cavity Raman laser using synthetic single-crystal diamond”, Optics・ Optics Express, 2010, Vol.18, No.16 M. P. Gaukroger et al., “Diamond and Related Materials”, Vol. 17, 2008, p. 262-269

  In light of the above, it should be understood that dislocations for certain properties that may or may not be consistent with the overall decrease in dislocation density, such as electronic and optical properties. There is a desire to find a way to minimize the impact. For example, in some applications (eg, applications that require mechanical toughness), high dislocation density may be preferred in nature, but the direction and / or type of dislocations is important for the functional performance of the material It may be. Therefore, there is a need to find a technique for engineering (manipulating) the type and / or direction of dislocations in homoepitaxially grown single crystal CVD synthetic diamond.

  The purpose of certain embodiments of the invention is to at least partially solve the above-mentioned problems.

  According to a first aspect of the present invention, a single crystal CVD synthetic diamond layer having a non-parallel dislocation array, wherein the non-parallel dislocation array is an array of cross-cross dislocations as viewed under X-ray topographic cross-section or luminescent conditions. There is provided a single crystal CVD synthetic diamond layer characterized by comprising a plurality of dislocations forming.

For certain applications, preferably the thickness of the single crystal CVD synthetic diamond layer is 1 μm or more, 10 μm or more, 50 μm or more, 100 μm or more, 500 μm or more, 1 mm or more, 2 mm or more, or 3 mm or more. Alternatively or additionally, the single crystal CVD synthetic diamond layer may be 10 cm ⁻² to 1 × 10 ⁸ cm ⁻² , 1 × 10 ² cm ⁻² to 1 × 10 ⁸ cm ⁻² or 1 × 10 ⁴ cm ^{−. 2} to 1 × 10 ⁷ cm ⁻² dislocation density and / or 5 × 10 ⁴ or less, 5 × 10 ⁻⁵ or less, 1 × 10 ⁻⁵ or less, 5 × 10 ⁻⁶ or less, or 1 × 10 ⁻⁶ or less It is good to have refraction. Embodiments of the present invention can be provided for a given range of possible non- {100} oriented single crystal diamond substrates, such as {110}, {113} and {111} oriented substrates, although certain For the above applications, it is preferable to use a substrate with {110} or {113} orientation. One or more of these features are advantageous in achieving a relatively thick and / or high quality layer of single crystal CVD synthetic diamond. For example, as a result of growth on a {111} oriented substrate containing a high concentration of dislocations formed in a single crystal CVD synthetic diamond layer, poor quality and strain that cannot be easily grown to large thickness without breakage May result in large material.

  Preferably, the non-parallel dislocation array extends over a significant volume of the single crystal CVD synthetic diamond layer, wherein the significant volume is at least 30%, at least 40%, at least 50%, at least 60% of the total volume of the single crystal CVD synthetic diamond layer. , At least 70%, at least 80% or at least 90%. The non-parallel dislocation array has a first set of dislocations that propagate in a first direction through the single crystal CVD synthetic diamond layer and a second set that propagates in the second direction through the single crystal CVD synthetic diamond layer. The angle formed between the first direction and the second direction is 40 ° to 100 °, 50 ° to 100 °, or 60 ° to 90 ° when viewed under an X-ray topographic sectional view or luminescent conditions. is there. Since dislocations are known not to propagate in a perfectly straight line state, the direction in which the dislocation propagates is measured as an average direction over the significant length of the dislocation, and the significant length is the total length of the dislocation. At least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80% or at least 90% and / or at least 50 μm, at least 100 μm, at least 250 μm, at least 500 μm, at least 1000 μm, at least 1500 μm Or at least 2000 μm.

  According to certain embodiments, not all dislocations in the material propagate in the manner described above. However, in certain embodiments, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80% of the total number of visible dislocations within the significant volume of the single crystal CVD synthetic diamond layer. % Or at least 90% form non-parallel dislocation arrays when viewed under X-ray topographic cross-sectional or luminescent conditions, and the significant volume is at least 30%, at least 40%, at least 50% of the total volume of the single crystal CVD synthetic diamond layer %, At least 60%, at least 70%, at least 80% or at least 90%.

  In certain embodiments, such as {110} oriented materials, non-parallel dislocation arrays are visible in x-ray topographic cross-sections but not under luminescent conditions. In certain alternative embodiments, such as {113} oriented materials, non-parallel dislocation arrays are visible under luminescent conditions, but not in X-ray topographic cross-sectional views. This is because dislocations in one particular line direction emit blue luminescent light (resulting in blue emission), while in other line directions, dislocations do not emit that way.

  In addition to the above, the materials having non-parallel dislocation arrays described herein should have good wear resistance combined with increased hardness (eg, at least 100 GPa, more preferably at least 120 GPa). There was found.

  According to another aspect of the invention, a single crystal CVD synthetic diamond object comprising the single crystal diamond layer described above, wherein the single crystal diamond layer is at least 30%, at least 40% of the total volume of the single crystal CVD synthetic diamond object. %, At least 50%, at least 60%, at least 70%, at least 80% or at least 90%. Such objects can be used in optical devices or applications, mechanical devices or applications, luminescent devices or applications and / or electronic devices or applications. As a variant, the single crystal CVD synthetic diamond object may be cut into a jewel form.

According to yet another aspect of the present invention, a method of forming a single crystal CVD synthetic diamond layer comprising:
Providing a single crystal diamond substrate having a growth surface with a defect density of 5 × 10 ³ / mm ² or less as revealed by plasma exposure etching;
Growing a single crystal CVD synthetic diamond layer according to any one of claims 1 to 12 on a growth surface.

  The growth surface of the single crystal diamond substrate should have a {110} or {113} crystal orientation to form a layer of single crystal CVD synthetic diamond material having a {110} or {113} orientation for the reasons described above. The growth rate of the single crystal CVD synthetic diamond layer is controlled to be low enough to form a non-parallel dislocation array. In this regard, at low growth rates on {110} oriented substrates, dislocations form a non-parallel dislocation array, whereas a parallel network of dislocations can be formed when the growth rate is increased. found. In the {110} orientation, non-parallel dislocations are grown by growing a single crystal CVD synthetic diamond layer on the {110} growth plane at a ratio of <110> growth rate to <001> growth rate below a certain limit. An array can be formed. A similar explanation is considered to apply to the {113} orientation. However, initial results indicate that relatively high growth rates can be utilized with {113} oriented substrates, while non-parallel dislocation arrays can still be achieved.

  According to certain embodiments, the non-parallel dislocation array includes a significant number of dislocations propagating at an acute angle of at least 20 ° relative to the growth direction of the single crystal CVD synthetic diamond layer, wherein the significant number is X At least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80% or at least 90% of the total number of dislocations visible under line topographic cross-sectional or luminescent conditions. More preferably, a significant number of dislocations propagate at an acute angle of 20 ° to 60 °, 20 ° to 50 ° or 30 ° to 50 ° with respect to the growth direction of the single crystal CVD synthetic diamond layer.

FIG. 5 is a flow diagram showing how various types and orientations of dislocations can be realized in CVD synthetic diamond, and in particular, an approach that can achieve a non-parallel array of dislocations in CVD synthetic diamond material. FIG. FIG. 5 illustrates method steps performed in forming a CVD synthetic diamond material having a non-parallel dislocation array in accordance with an embodiment of the present invention, and another possible synthesis technique that results in a parallel array of dislocations. It is a figure which shows the dislocation type which propagates in the direction parallel to the growth direction in a (110) growth CVD synthetic diamond layer. It is a figure which shows the dislocation type which makes an acute angle and propagates with respect to the growth direction in a (110) growth CVD synthetic diamond layer. FIG. 2 shows a single crystal CVD synthetic diamond layer including a parallel array of dislocations. FIG. 2 shows a single crystal CVD synthetic diamond layer including a non-parallel array of dislocations. It is a figure which shows the birefringence photomicrograph regarding the CVD synthetic diamond material of FIG. FIG. 2 is a cross-sectional view of an X-ray topography and shows a single crystal CVD synthetic diamond layer grown on {110} and {113} oriented substrates under luminescent conditions.

  In accordance with certain embodiments of the present invention, the inventors have developed techniques for producing single crystal CVD synthetic diamond, particularly high quality single crystal CVD synthetic materials, having non-parallel dislocation arrays. This differs from the prior art in that the parallel array of dislocations is the production of CVD synthetic diamond that occurs in the direction of growth of the CVD synthetic diamond film. A parallel array of dislocations has proven to be a source of some problematic influences. For example, as a result of parallel arrays of significant density of dislocations, strain and birefringence in the material reduce its performance for optical applications, such as Raman lasers. A parallel array of dislocations can adversely affect the toughness and / or wear resistance of the diamond material. Furthermore, parallel arrays of dislocations can also adversely affect the luminescence and electronic and electro-optical (photoelectron) properties of CVD synthetic diamond. In addition, in the case of diamond detectors, some workers have speculated that certain types of dislocations can serve as carrier traps and reduce the breakdown voltage.

  Prior work has been aimed at minimizing the density of dislocations in CVD synthetic diamond material. In contrast, the present invention has focused on providing a non-parallel array of dislocations propagating in various directions to form a cruciform array of dislocations. The presence of non-parallel dislocation arrays can be beneficial for certain types of optical devices. This is because it results in a lower overall strain morphology, which reduces the birefringence in the CVD synthetic diamond layer. The presence of non-parallel dislocation arrays can also increase the toughness and / or wear resistance of CVD synthetic diamond materials. Furthermore, the presence of non-parallel dislocation arrays can also improve electronic performance. For example, certain types of dislocations can propagate in preference to other types, and such certain types of dislocations act as carrier traps and reduce breakdown voltages.

Certain embodiments of the present invention can be utilized with various chemical types of CVD synthetic diamond materials, such as nitrogen doped, phosphorus doped, boron doped and undoped CVD synthetic diamond. Examples include, but are not limited to, materials. Several experimental techniques can be utilized to show that the diamond material is inherently CVD synthesized. Examples include (but are not limited to): emission at 466 nm and / or 533 nm and / or 333 nm in the photoluminescence spectrum measured at 77 K using 325 nm, 458 nm or 514 nm continuous wave laser excitation. The presence of a feature or the presence of an absorption feature at 3123 cm ⁻¹ in the infrared absorption spectrum. Publication by PM Martineau et al., “Gems & Gemology”, 40 (1) 2, 2004, whether diamond materials are CVD synthesized. And provides an example of a CVD synthetic diamond material that has been grown and / or annealed under a wide variety of conditions.

  The term “layer” refers to any growth region of CVD synthetic diamond, and also refers to a free-standing CVD synthetic diamond material originally made by deposition of a layer on a substrate and optionally a substrate that is later removed. I mean. A single crystal CVD synthetic diamond object comprising the single crystal diamond layer described above can be provided, wherein the single crystal diamond layer is at least 30%, at least 40%, at least 50%, at least of the total volume of the single crystal CVD synthetic diamond object. 60%, at least 70%, at least 80% or at least 90%.

  A non-parallel dislocation array uses a technique (eg, X-ray topography, electron microscopy or luminescent imaging) that can image dislocations in a significant volume of CVD synthetic diamond material in a cross-sectional view to: That is, (i) one set of dislocations propagates in a single crystal CVD synthetic diamond layer in a first direction, and another set of dislocations propagates in a single crystal CVD synthetic diamond layer in a second direction. There are two or more linear dislocations (ie not all having the same linear direction), (ii) there are dislocations belonging to the first and second sets Appear to cross each other, (iii) the angle between the first direction and the second direction is 40 ° to 100 °, 50 ° to 100 °, or 60 ° to 90 ° when viewed in cross-section Can be observed It means the door. The significant volume of the CVD synthetic diamond material is preferably at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80% or at least 90% of the total volume of the CVD synthetic diamond material. In a significant volume, preferably at least 30%, more preferably at least 50%, more preferably at least 70%, and most preferably at least 90% of the dislocations in the CVD synthetic diamond layer propagate as described above.

  It may be useful to characterize nonparallel dislocations by comparing the line direction of nonparallel dislocations with a CVD synthetic diamond growth direction that can be determined by examining the orientation of certain point defects within the crystal lattice. . For example, defects such as nitrogen-vacancy (NV) and nitrogen-vacancy-hydrogen (NVH) complexes align along the <111> direction, giving eight possible morphologies (+ ve line direction), these morphologies The relative population may have a preferential orientation relative to the growth direction. Electron paramagnetic resonance measurements that change the angular alignment of the magnetic field are used to examine the orientation of these defects. For example, the inventor found that during growth on the (110) surface, both of these defects were mostly oriented along two <111> orientations located out of plane with respect to the (110) growth plane ( 50% or more, 60% or more, 80% or more, 95% or more, or even 99% or more). This preferential defect alignment is not observed for identical defects (eg, NV) in a sample grown on a substrate with a substantially {100} orientation. Since the symmetry of the relationship between the <111> direction in which these defects are located and the main growth plane for CVD diamond containing {100}, {110} and {111} is unambiguous, the characteristics of the defect population distribution By using the attachment, it is possible to unambiguously define the growth direction, in particular to determine whether growth has occurred on the {110} plane and to identify the exact {110} plane of growth in this material. . Non-parallel dislocations are 20 relative to the growth direction (the growth direction is typically perpendicular to the main {110} CVD growth plane which is typically parallel to the substrate, but not always). It can propagate with an acute angle of between 60 ° and 60 ° or preferably between 20 ° and 50 ° or more preferably between 30 ° and 50 °, the significant volume being 30%, 40% of the total volume of the CVD synthetic diamond material, 50%, 60%, 70%, 80% or 90%.

  There already exists a method for producing CVD diamond having two or more different regions of growth that are different from each other, with each region having parallel dislocations with each region propagating in a certain linear direction. It is defined by having a dislocation in one region that propagates to a dislocation in another region, apparently parallel to another direction. Thus, it is suggested that dislocations in one region are not parallel to dislocations in another region. An example of two different regions is when a secondary CVD synthetic diamond layer is grown on a CVD synthetic diamond substrate and the initial growth direction of the substrate and the initial growth direction of the secondary CVD synthetic diamond layer are different (about this) Are described, for example, by MP Gaukroger et al., “Diam. Relat. Mater.”, Vol. 17, 2008, p. 262. See). In this case, the substrate and the secondary layer are two different regions. Another example of different regions is the growth of CVD synthetic diamond on off-axis substrates in which individual dislocations change substantially and abruptly in these line directions by crossing different growth pseudosectors. In this case, a dislocation in one pseudo sector corresponds to a dislocation in one region, and a dislocation in another pseudo sector corresponds to a dislocation in another region. Dislocations that are not parallel to each other in the same region of material, i.e., dislocations in different regions of CVD synthetic diamond material that effectively form two separate parallel arrays without crossing each other in different regions of the material. This differs from aspects of the present invention relating to the provision of dislocations that cross each other to form a nonparallel array.

  Dislocations in diamond can be located using X-ray topographs recorded using a Lang camera attached to an X-ray generator. With the cross-sectional topograph recorded using Bragg reflection of the {533} crystal plane, the sample can be set up so that the plane sampled by the X-ray beam is located within 2 {001} flatness. The {110} plane can be sampled by the cross-sectional topograph recorded using the Bragg {008} reflection. X-ray sections and projection topography have been extensively utilized for diamonds by Lang et al. (For example, see I. Kiflawi et al., “Phil. Mag.” 33, No. 4, 1976, p. 697 and edited by AR Lang, JE Field, “The Properties of Diamond”. of Diamond), London, Academic Press, 1979, pp. 425-469). By using the cross-sectional X-ray topography image and the projected X-ray topography image, the dislocation line direction and most of the volume occupied by the dislocation can be measured. For example, by imaging (but not limited to) two or more cross-sectional topographies by imaging the {100} plane and the {110} plane, the angles and growth directions and dislocation lines that are formed by each other. The angle formed by the direction can be determined. Most volumes can be defined either by projection topographs or by two or more cross-sectional topographs.

The contrast visible in the X-ray topograph is due to strain applied on the crystal lattice by dislocations or dislocation bundles. Advantageously, by sampling an area of 10 nm ^{2 to 1} mm ² of a single crystal CVD synthetic diamond article containing non-parallel dislocations, this area has a dislocation / dislocation bundle density of 10 to 1 × 10 ⁸ cm ^−2. You can be sure that In X-ray topographs, it is difficult to distinguish dislocation and dislocation bundles, but the strong contrast in the image usually means the latter dislocation bundle. Therefore, “dislocation” and “dislocation bundle” are often used interchangeably. Analyzing the recorded projection topograph by translating the sample into the X-ray beam can provide information on the number of dislocations throughout the sample (for example, MP Goukuroger, et al. ( MP Gaukroger et al.), "Diamond and Related Materials", Vol. 17, 2008, p.262-269).

  In addition to the dislocation concentration, the linear direction and / or Burgers vector (ie, the type of dislocation) can also be said to play an important role. It should be noted that when we say the type of dislocation, this means the angle of the Burgers vector with respect to the dislocation line direction. In an edge dislocation, the Burgers vector and the dislocation line are perpendicular to each other (ie, 90 °). In the screw dislocation, the Burgers vector and the dislocation line are parallel to each other (that is, 0 °). In mixed dislocations, the Burgers vector is directed at an acute angle between 0 ° and 90 °. The type of dislocation is confirmed by analysis of stored X-ray topographs for a wide variety of reflections (for example, by MP Gaukroger et al., “Diamond (See Diamond and Related Materials, Vol. 17, 2008, p.262-269). This type of analysis can be used in characterizing a single dislocation, but if a bundle is present, the analysis can be complex because the bundle may contain more than one type of dislocation. In this case, another type of dislocation bundle (not including a single major type) cannot be characterized for a particular dislocation type and is excluded from the analysis.

  Different dislocation types have different degrees of atomic recombination from one another and thus give more or less dangling bonds, which may contribute to or affect the optoelectronic properties. There is. For example, the presence or absence of blue dislocation photoluminescence present in CVD synthetic diamond materials can likely depend on both the dislocation line direction and its Burgers vector, ie, certain dislocation types exhibit luminescent luminescence. But other things are not. This further intensifies the inventor's interest in being able to select and control dislocation types in CVD synthetic diamond materials.

  As can be seen, each dislocation does not tend to propagate along a perfectly straight line, unlike the step that occurs during the growth of a CVD synthetic diamond layer that causes the formation of terraces and risers. This deviates from such a perfect straight line. For the effect of steps on dislocations in CVD synthetic diamond, see Martyau et al., “Phys. Status Solidi C6”, No. 8, 2009, p. . 1953-1957. Thus, as will be appreciated, the direction in which a dislocation propagates is described herein in terms of the average direction over the significant length of the dislocation, where the significant length is at least 30%, at least 40% of the total length of the dislocation. %, At least 50%, at least 60%, at least 70%, at least 80% or at least 90% and / or at least 50 μm, at least 100 μm, at least 250 μm, at least 500 μm, at least 1000 μm, at least 1500 μm or at least 2000 μm.

  A single crystal CVD synthetic diamond layer (eg, (110) orientation) may have a significant number of non-parallel dislocations oriented within the range of 20 °, 10 ° or 5 ° in the <100> line direction; A significant number is, for example, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80% or at least 90% of the total number of dislocations visible in either a cross-sectional topography or a projected topograph is there. Optionally, less than 70%, less than 60%, less than 50%, less than 40%, less than 30%, less than 20% or less than 10% of the dislocations within the significant volume of the single crystal CVD synthetic diamond layer are <110> linear Oriented within the range of 20 °, 10 ° or 5 °, and a significant number is at least 30%, at least 40%, at least 50%, at least, for example, the total number of dislocations visible in either a cross-sectional topography or a projected topograph 60%, at least 70%, at least 80% or at least 90%. The <100> dislocation may be either a 45 ° mixed type or a blade type. According to certain example configurations, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80% or at least of the total number of characterizable dislocations in the (110) orientation layer 90% are of the 45 ° type and / or the blade type. According to certain specific configurations, less than 70%, less than 60%, less than 50%, less than 40%, less than 30%, less than 20% of the characterizable dislocations in the significant volume of a single crystal CVD synthetic diamond layer. Less than 10% or less than 5% is of the <110> mixed 60 ° type. Further, according to certain specific configurations, less than 70%, less than 60%, less than 50%, less than 40%, less than 30% of the characterizable dislocations in the significant volume of the single crystal CVD synthetic diamond layer, 20% Less than 10%, less than 5% or less than 5% may be of the <110> spiral type or <110> blade type.

  It is important to note that the above percentage of dislocation types is relative to the total number of dislocations that can be characterized as having a particular type in a given analytical method. For example, as described above, dislocation bundles with a wide variety of dislocation types (not including a single major type) are not characterizable using topographic analysis methods, and thus are not characterizable. Discarded. This is understood by those skilled in the art and is described in detail below.

  The dislocation Burgers vector can be categorized by collecting a wide variety of projected X-ray topographs. In order to create a projection topograph, it is necessary to translate the sample into the x-ray beam to expose its full volume and to translate the membrane accordingly to maintain its position relative to the sample. X-ray projection topographs using various Bragg reflections are used to categorize Burgers vectors of dislocation-related features in the X-ray topographs. An overview of this method is given by M. P. Gaukroger et al., “Diamond and Related Materials”, Vol. 18, 2008, p. 262-269. For diamond, the <110> Burgers vector is assumed. In general, the contrast of dislocation-related features is determined by the angle between the Burgers vector and the atomic layer that causes the diffraction. As a good approximation, dislocation-related features are not visible in a given x-ray topograph if the Burgers vector is located parallel to the diffractive surface, and if the Burgers vector is located perpendicular to the diffractive surface. It has a strong contrast and has a medium contrast when its Burgers vector is located at an intermediate angle of 0 ° to 90 ° with respect to the diffractive surface, which contrast is close to 90 ° for the Burgers vector. Strong when the Burgers vector is close to 0 °. This means that different dislocation types with different Burgers vector directions have different contrasts in a particular topographic image. Furthermore, a single transposition feature having a particular Burgers vector direction exhibits different contrasts in topographic images taken in different directions relative to that Burgers vector.

  By this method it is possible to locate the Burgers vector of a given diffraction related feature and thus characterize its type. Dislocation features that include a large number of dislocations with different Burgers vectors (not having a major direction) tend to have moderate contrast in different topographic images taken in different directions and characterize this It will not be possible.

  In practice, other factors must be taken into account. Reflections must also be selected in order to create a suitable perspective for the purpose of clearly imaging the dislocation and to accurately determine the position of the dislocation between different topographies. The {111} reflection is a good reflection for conventional growth on a (100) substrate, but this is not an optimal reflection in other cases. For this task, it has been found problematic to use {111} reflections in order to create an appropriate perspective view so that individual dislocation-related features can be accurately resolved. Therefore, {220} reflection is selected. This is because it provides a near “plan” view (approximately 14 ° off-axis) of the sample, which makes it easy to recognize the same dislocation in another view. When four projection topographs using {220} reflection with a growth direction of [110] are used, from (202) plane, (022) plane, (02-2) plane, and (20-2) plane Record four topographs using reflection. If the Burgers vector is located in one of the diffractive {220} planes, the dislocation has a strong contrast in one topograph, a moderate contrast in the adjacent topograph, and a fourth It is expected to be invisible on the topograph. If the dislocation-related features are purely bladed or purely helical, it is expected that there will be moderate contrast in all four topographs. In this case, in order to distinguish the two, it is necessary to take a topograph using (110) reflection in the growth surface. Using this method, different types of dislocations can be characterized. In the case of dislocation bundles containing different dislocation types, the bundles tend to have moderate contrast in all topographic images and cannot be characterized. Such dislocation features are discarded from the analysis. In the case of primarily one type of dislocation bundle, the bundle has different contrasts in different topographies according to the main type of dislocation within the bundle, which could be characterized. Such a dislocation feature is considered as a single dislocation for many analytical purposes. In order to determine the presence or absence of dislocation-related features in several X-ray topographs, it is necessary to accurately match the dislocation-related contrast in different images. This can be done manually by visual inspection or can be automated using a suitable computer algorithm.

  Embodiments of the present invention provide for the source of the next dislocation in the CVD synthetic diamond: (i) threading dislocation from the primary (substrate) layer to the secondary CVD synthetic diamond layer and (ii) surface defects or other reasons (e.g. This is based on the inventor's understanding that there are two mechanisms that can locate dislocations that occur as nuclei at the interface between the substrate surface and the CVD synthetic diamond layer due to lattice mismatch. What led to certain embodiments of the present invention is the finding that growth on the (110) surface provides a tremendous amount of dislocation engineering techniques for both (i) and (ii).

表２：（００１）成長後の垂直方向にスライシングされた一次ＣＶＤ層上の（００１）成長は、転位がそれぞれ［１１０］及び［０１０］線方向である場合に種々の貫通転位タイプを示す。 With regard to item (i), certain embodiments of the present invention include slicing a primary (001) CVD layer vertically to form a growth plane (110) and growing on this growth plane ( 110) Based on studies performed by the inventors in examining growth on the surface. The inventor changes the line direction as shown in Table 2, but maintaining the Burgers vector results in one type of dislocation in the primary (001) growth layer being secondary (110). It has been recognized that there is a mathematical argument that penetrates into the growth layer and is converted into a second type of dislocation therein. From this table it is observed that it is possible to form a secondary CVD layer that includes only a specific dislocation type and / or line direction. For example, if the primary (110) growth layer contains 45 ° mixed dislocations, it is possible to form a CVD layer containing 60 ° mixed <110> dislocations. Conversely, if the primary (001) growth layer contains edge dislocations, it is possible to make a secondary (110) growth layer containing 45 ° mixed <100> dislocations. Thus, it has been demonstrated that it is possible to engineer a particular dislocation line direction and type in the secondary CVD layer defined by the dislocation type in the primary layer. This possibility of growing several types / line directions of threading dislocations, among others, gives the possibility to study different types of dislocations (edge dislocations, helical dislocations or mixed dislocations) separately. This provides a much wider range of application in terms of dislocation engineering than standard growth on (001) substrates.

Table 2: (001) growth on vertically sliced primary CVD layer after (001) growth shows various threading dislocation types when the dislocations are in the [110] and [010] line directions, respectively.

  In connection with item (ii) above, the inventors have observed that the growth on the (110) surface gives a broader scope allowing dislocation engineering for dislocations occurring at the CVD / substrate interface. did. The inventor can make a non-parallel array of dislocations with a <100> direction under certain growth conditions described later, if a good (110) surface finish is employed for (110) growth, We have observed that some of these dislocations are nucleated at the interface between the (110) substrate and the secondary layer. However, when a poor or poor substrate surface finish is employed, a parallel array of dislocations with <110> directions is observed regardless of the growth conditions. Poor substrate surface finishes cause microscale cracks on the substrate surface that act as dislocation sources, and the inventor is of the specific type that these dislocations nucleated at surface defects grow in parallel <110> morphology Observed that. However, it is essential to carefully treat the substrate surface to avoid nucleation of these parallel dislocations.

One particular method of forming a single crystal CVD synthetic diamond layer is to provide a single crystal diamond substrate with a (110) growth surface having a defect density of 5 × 10 ³ / mm ² or less as revealed by plasma exposure etching. Preparing and growing a single crystal CVD synthetic diamond layer on a (110) growth surface at a ratio of <110> growth rate to <001> growth rate that is less than the limit, whereby a non-parallel dislocation array becomes a single crystal CVD synthetic diamond layer To occur inside. The (110) growth surface can be formed from single crystal CVD synthetic diamond, single crystal natural diamond or single crystal HPHT (high pressure high temperature) synthetic diamond. For example, a single crystal CVD synthetic diamond plate, a single crystal natural diamond or a single crystal HPHT synthetic diamond plate is treated and revealed by plasma exposure etching to have a defect density of 5 × 10 ³ / mm ² or less (110) growth surface Can be formed. Examples of the treatment include slicing and polishing and / or plasma etching.

According to certain embodiments, a multi-stage growth process can be utilized. For example, one particular method is
Providing a single crystal diamond substrate with a (001) growth surface as revealed by plasma exposure etching and having a defect density of 5 × 10 ³ / mm ² or less;
(001) growing a first single crystal CVD synthetic diamond layer on the growth surface; (110) forming a growth surface by slicing the first single crystal CVD synthetic diamond layer vertically;
(110) treating the growth surface such that it has a defect density of less than 5 × 10 ³ / mm ² as revealed by plasma exposure etching;
Growing a second single crystal CVD synthetic diamond layer on the (110) growth surface at a ratio of <110> growth rate to <001> growth rate below the limit, whereby the non-parallel dislocation array is the second single crystal CVD. To occur in the synthetic diamond layer.

  FIG. 1 is a flow diagram showing how various types and orientations of dislocations can be realized in CVD synthetic diamond, in particular achieving a non-parallel array of dislocations in CVD synthetic diamond material. It is a figure which emphasizes and shows the technique which can do. In FIG. 1, the primary layer means a (001) single crystal CVD synthetic diamond layer grown on a (001) single crystal diamond substrate. Next, the primary layer is sliced vertically along the diagonal to form a (110) single crystal diamond substrate, and a (110) single crystal CVD synthetic diamond secondary layer is grown thereon.

  It should be noted that when describing a (001) single crystal diamond substrate, it means that the substrate is oriented to have a (001) crystal plane at the growth plane. However, the growth plane may not be perfectly aligned with the (001) oriented plane. Due to processing constraints, the actual growth plane orientation may differ from this ideal orientation by up to 5 ° and in some cases up to 10 °. However, this is less desirable because it adversely affects reproducibility. Similar explanations apply to (110) single crystal diamond substrates.

  FIG. 1 highlights that the dislocation type found in the primary layer is determined by the quality of the (001) substrate growth surface on which the primary layer was grown. If the surface finish of the (001) substrate growth surface is poor or poor, mixed 45 ° dislocations are formed in the <001> direction (ie, parallel arrays with mixed 45 ° orientation are aligned perpendicular to the growth direction). When the surface finish of the (001) substrate growth surface is good, edge dislocations are the main type formed in the <001> direction (ie, parallel arrays are aligned perpendicular to the growth direction).

  FIG. 1 shows that the type and orientation of dislocations found in the secondary layer are (i) the type of dislocations in the primary layer, (ii) the surface finish of the (110) substrate made from the primary layer, and (iii) the secondary. It also shows that it may depend on the growth rate used for the layer.

  A poor substrate growth surface finish is first applied to the growth of the primary layer resulting in a <100> mixed 45 ° parallel array, and then the primary layer is sliced vertically along the diagonal (110 ) When a single crystal diamond substrate is formed and a secondary layer is grown thereon, a parallel array of <110> orientation dislocations of mixed 60 ° type is created. This is an undesirable way.

  In contrast, if a good substrate growth surface finish is initially applied for the growth of the primary layer, the result is a parallel array of <100> edge dislocations, and then the primary layer is diagonalized. When forming a (110) single crystal diamond substrate by vertically slicing along and growing a secondary layer thereon, the inventor has many possibilities as shown in FIG. I found that it can be used. If the surface finish of the (110) single crystal diamond substrate (on which the secondary layer is grown) is poor or poor, again, due to surface defects, the mixed 60 ° type parallel <110> orientation dislocations Occurs. When the (110) single crystal diamond substrate is sufficiently pretreated, there are surprisingly two possibilities depending on the growth rate of the secondary layer. If a relatively high ratio of <110> growth rate to <001> growth rate is used for the secondary layer, a parallel array of <110> oriented spirals and / or edge-type dislocations is created. As a variant, if a relatively low ratio of <110> growth rate to <001> growth rate is used for the secondary layer, a non-parallel array of <100> orientation 45 ° and / or edge-type dislocations Is made.

  (110) It may be important to avoid surface defects on the substrate. This is because, as a result of these surface defects, the low core energy form, ie, <110> mix 60 ° (the <100> mix formed during growth on a standard (001) substrate with poor pre-treatment. This is because nucleation of new dislocations exhibiting (similar to 45 ° dislocations) occurs in the secondary layer. In order to avoid nucleation of <110> mixed 60 ° dislocations in the secondary layer, it was well pre-treated by using pre-etching prior to growth, for example by skiff polishing and avoiding macroscopic pits (110 ) Growth on the substrate is necessary.

  Even if the (110) substrate for the secondary layer is fully pretreated and the surface defects are negligible, at the interface between the (110) substrate and the secondary CVD synthetic diamond layer There are some more non-threading dislocations that originate. Without being bound by theory, except for the above mechanism of dislocation nucleation, these defects may be due to lattice parameter mismatches between the primary and secondary layers. . It has been observed that even though these dislocations originate at the interface in the same way as dislocations caused by poor substrate pretreatment, these dislocations arise due to poor substrate pretreatment. Unlike dislocations, it exhibits a non-parallel array of 45 ° or edge type morphology with <100> orientation. Accordingly, these dislocations need not be removed to achieve embodiments of the present invention.

  In light of the foregoing, in order to achieve a non-parallel array of dislocations in single crystal CVD synthetic diamond in accordance with certain embodiments of the present invention, (i) prior to the growth of the primary (001) diamond layer. The need for careful pretreatment of the initial (001) substrate, (ii) careful pretreatment of the (110) substrate formed from the primary layer, and (iii) careful control of the growth rate of the secondary (110) diamond layer it is obvious.

  Without being bound by theory, the above results can be justified as follows.

  CVD single crystal diamond growth is usually determined by kinematics rather than thermodynamic processes. However, the balance between kinematics and thermodynamic processes can be changed by changing growth parameters. For example, by growing at a ratio of low <110> growth rate to <001> growth rate, growth is likely to be dominated by thermodynamic factors rather than kinematic factors, and high <110> If the ratio of the growth rate to the <001> growth rate is high, the reverse relationship holds.

  In addition to the above, the inventor should have a <110> growth rate and <001> growth rate "low" ratio of less than 1.0, and a "high" ratio of 1.0. I found it better to exceed. The ratio between the <110> growth rate and the <001> growth rate may be controlled to be 1.0 or less, 0.8 or less, 0.6 or less, 0.4 or less, or 0.2 or less. However, those skilled in the art will appreciate that various conditions, such as different diamond growth surface temperatures, affect the detailed kinematics / thermodynamics and substantially alter this definition of “low” and “high”. You will recognize that there are cases. The ratio between the <110> growth rate and the <001> growth rate is strongly influenced by the <110> growth rate.

  It is possible for those skilled in the art to change the ratio of <110>: <001> growth rate in the manner described above. Previously published work discusses changes in growth parameters such as nitrogen doping, boron doping and their relative effects on substrate temperature and growth rates in different crystal directions. Such a growth rate ratio is usually characterized by an α parameter, a β parameter and a γ parameter. However, for the purposes of the present invention, this is a complex theme and only needs to mention the growth rate ratio of <110>: <100>.

  By growing a secondary layer of (110) CVD synthetic diamond at a sufficiently low <110>: <100> growth rate ratio, the dislocations are configured to minimize their total energy per unit length. Can be adopted. That is, low core energy (more thermodynamically desirable) dislocations are grown per unit length. <110> mixed 60 ° dislocations are expected to have the lowest energy per unit length. Thus, under a low <110>: <100> growth rate ratio, the <100> mixed 45 ° dislocations in the primary layer are penetrated through the secondary layer or before the surface of the (110) substrate made from the primary layer. If these <110> mixed 60 ° dislocations can be caused either due to poor processing, such <110> mixed 60 ° dislocations are still grown. It is therefore desirable to remove all sources of <110> mixed 60 ° dislocations. As noted above, this is an accurate pre-treatment of the substrate on which the primary layer is grown to minimize <100> mixed 45 ° dislocations in the primary layer and the good of the (110) substrate made from the primary layer. This is done by both surface pretreatment.

  Growing a non-parallel array of <100> oriented edge dislocations and mixed 45 ° dislocations in the absence of the <110> mixed 60 ° dislocations to be made. Edge dislocations in the <100> orientation and mixed 45 ° dislocations propagate at an acute angle of about 45 ° from the growth direction, resulting in a non-parallel dislocation array. This was achieved by a combination of accurate primary and secondary substrate processing and secondary layer growth parameters.

  At high <110>: <100> growth rate ratios, the kinetic characteristics of the growth process outweigh the thermodynamic characteristics. If the growth process is dominated by kinematics rather than thermodynamics, the dislocations only return to the shortest length form, which means that they are in the growth direction, i.e. in this case for the secondary layer < 110> means to follow the direction. Thus, at high growth rates, high core energy dislocations grow preferentially. These dislocations include <110> helical dislocations and <110> edge dislocations as shown in FIG.

  Details regarding how to pretreat the growth surface and how to control the growth rate to achieve the present invention are described later in this specification. It should be noted that the specific growth rate ratio required to achieve a non-parallel array of dislocations depends on the growth chemistry used in the CVD process and depends on the specific growth chemistry used. There will be minute variations. However, as will be appreciated, those skilled in the art can optimize the growth rate ratio by performing a series of tests at different growth rate ratios for a particular process setup, the purpose of which is Switches from thermodynamically stable <100> orientation to kinematically induced <110> orientation during secondary growth stage based on (110) substrate containing edge-type dislocations with <100> orientation The goal is to find a growth rate ratio that is close to the target limit but does not exceed it. Those skilled in the art know the factors that change the growth rate ratio. These include, for example, the diamond growth temperature, the carbon fraction in the gas phase, and the presence of certain impurities such as nitrogen and boron.

  FIG. 2 illustrates the method steps performed in forming a CVD synthetic diamond material having a non-parallel dislocation array according to an embodiment of the present invention, and another possible synthesis technique that results in a parallel array of dislocations. Initially, a (001) single crystal diamond substrate 2 is prepared. This can be made of natural diamond material, HPHT or CVD synthetic diamond material. Each of these different types of diamond material has its own distinct features, and thus can be identified as distinct, but an important feature of this substrate is that the growth surface has a good surface finish It has been carefully pretreated.

The term good surface finish has a surface with a defect density of 5 × 10 ³ / mm ² or less as revealed by plasma exposure etching. Defect density is most easily determined after using a plasma or chemical etch (referred to as plasma exposure etching) that has been optimized to reveal defects using, for example, a short-time plasma etch of the type described below. Characterized by optical evaluation of

  Two types of defects can be revealed by:

1) Defect inherent in substrate material quality. In selected natural diamonds, the density of these defects may be as low as 50 / mm ² , a more typical value is 10 ² / mm ² , and in others, such a value is It may be 10 ⁶ / mm ² or more.
2) Defects resulting from polishing (including dislocation structures and microcracks that form chatter trajectories along the polishing line). These densities can vary considerably from sample to sample, with typical values ranging from about 10 ² / mm ² up to 10 ⁴ / mm ² or more for poorly polished regions or samples.

A preferred low defect density is such that the density of the surface etch features associated with the defects is less than 5 × 10 ³ / mm ² , more preferably less than 10 ² / mm ² . It should be noted that simply polishing the surface to have a low surface roughness does not necessarily meet these criteria. This is because plasma exposure etching exposes defects at the surface and directly beneath it. In addition, plasma exposure etching can reveal inherent defects such as dislocations in addition to surface defects such as microcracks and surface features that can be removed by simple polishing.

Thus, the level of defects at and below the substrate surface where CVD growth occurs can be minimized by careful selection and pretreatment of the substrate. A process called “pretreatment” is a process applied to a material based on mining (in the case of natural diamonds) or synthesis (in the case of synthetic materials). This is because each step may affect the surface defect density in the material at the plane that will ultimately form the substrate surface when pretreatment as a substrate is completed. Specific processing steps include conventional diamond processes such as mechanical sawing, lapping and polishing (specially optimized for low defect levels in this application) as well as less conventional techniques, Examples include laser processing, reactive ion etching, ion beam milling or ion implantation and lift-off techniques, chemical / mechanical polishing, and both liquid chemical processing and plasma processing techniques. In addition, preferably, 0.08 mm surface R _Q measured by stylus profilometer over the length should be minimized, typical values prior to plasma etching, several nanometers or less, i.e., Less than 10 nanometers. R _Q is the root mean square deviation of the surface profile from flat (for a Gaussian distribution of surface height, R _Q = 1.25 Ra. For definition, see, for example, IM Hutchings, "See Tribology: Friction and Wear of Engineering Materials", Edward Arnold, 1992, ISBN 0-340-56184). .

One particular method of minimizing substrate surface damage is to perform in-situ plasma etching on the surface where homoepitaxial diamond growth is to occur. In principle, this etch need not be in situ and need not be immediately before the growth process, but the greatest advantage is achieved when it is in situ. This avoids the risk of further physical damage or chemical contamination. In-situ etching is also generally most convenient when the growth process also utilizes a plasma. Plasma etching is a similar condition to the deposition or diamond growth process, but the use of a slightly lower temperature condition is generally not present to provide good control of the etch rate without the presence of carbon containing source gases. good. For example, plasma etching may comprise one or more of the following techniques.
(I) Oxygen etching using primarily hydrogen but optionally using a small amount of Ar and the required small amount of O ₂ . Typical oxygen etching conditions are a pressure of 50-450 × 10 ² Pa, an etching gas with an oxygen content of 1-4 percent, an argon content of 0-30 percent and the balance hydrogen, all proportions being The substrate temperature is 600 to 1100 ° C. (more typically 800 ° C.), and the typical duration is 3 to 60 minutes.
(Ii) Hydrogen etching similar to (i) but without oxygen present.
(Iii) Another etching method that does not use only argon, hydrogen, and oxygen, for example, an etching method using halogen, other inert gas, or nitrogen can be used.

  Typically, such etching involves oxygen etching, then hydrogen etching, and then proceeds directly to synthesis by introducing a carbon source gas. The etching time / temperature can remove the remaining surface damage caused by the process and can remove surface contaminants, but does not produce a very rough surface and crosses the surface. Thus, it is chosen not to etch extensively along long defects, such as dislocations, which produce deep pits. Because of the strong etching, it is particularly important for this stage that the chamber design and material selection of its components are such that no material is transferred from the chamber to the gas phase or to the substrate surface by the plasma. The hydrogen etch following the oxygen etch is less specific to the crystal result and rounds off the angular accuracy caused by the oxygen etch that severely attacks such defects, providing a smooth and good surface for subsequent growth. .

  As shown in FIG. 2, the growth surface of the (001) single crystal diamond substrate 2 is appropriately pretreated, and in step A, the primary layer 4 of the (001) oriented single crystal CVD synthetic diamond material is formed on the substrate 2. CVD growth is performed. This layer will contain edge-type dislocations of <100> orientation as described above in connection with FIG.

  In step B, the primary layer 4 of the (001) oriented single crystal CVD synthetic diamond material is sliced vertically along a diagonal (shown in dotted lines in FIG. 1) as shown in step C. (110) A single crystal diamond plate 6 is obtained. This can be achieved using a laser. Next, a (110) single crystal diamond plate 6 is preferably used as a substrate, and a secondary layer 8 of single crystal CVD synthetic diamond material is grown on this substrate. A secondary layer of single crystal CVD synthetic diamond material can then be grown on the growth surface of the (110) substrate.

The growth surface of the (110) substrate 6 must be processed in the same manner as described in connection with the (001) substrate to obtain a good surface finish. The expression good surface finish again means that the surface has a defect density of 5 × 10 ³ pieces / mm ² or less, more preferably 10 ² pieces / mm ² or less as revealed by plasma exposure etching. I mean. However, excessive etching of the substrate results in pits on the substrate surface. Typically, these pits consist of (001) and (111) crystal planes, and if these pits are deeper than 5 μm, the pits result in low energy (ie, <110> mixing 60 °) New dislocation nucleation adopting the morphology will occur in the (110) layer. This also manifests itself as a pit on the final growth surface. The conditions for overetching vary greatly depending on the geometry of the reactor, but occur when etching with excessive duration (several hours) or excessive power and / or temperature.

  Various possibilities for the type and orientation of the dislocation are shown in steps D, E, F of FIG. According to Step D, if the initial (001) diamond substrate was not pretreated well and, as a result, <100> mixed 45 ° dislocations occurred in the primary layer, A parallel array 10 of mixed 60 ° dislocations may be nucleated in the secondary layer. According to Step E, the initial (001) diamond substrate is pretreated well, and as a result, <100> edge dislocations occur in the primary layer, but with high <110> growth rate and <001> growth rate. When the ratio is used to form the secondary layer 8, a parallel array 12 of <100> oriented spirals and edge dislocations is formed in the secondary layer. In contrast, according to Step F, the initial (001) diamond substrate was well pretreated, resulting in <100> edge dislocations in the primary layer, but relatively low <110>. When the ratio of growth rate to <001> growth rate is used to form the secondary layer 8, a <100> orientation mix of 45 ° and a non-parallel array 14 of edge dislocations is formed in the secondary layer. .

Growth on the (110) substrate as described above provides a way to produce a wider variety of dislocation types in the secondary layer than growth on the (001) surface. The possible orientations and types of dislocations in the secondary (110) layer are summarized below.
Linear direction Dislocation type (assuming <110> Burgers vector)
[100] → edge shape [100] → mixing 45 °
[110] → 60 ° mixing (most desirable in terms of core energy)
[110] → edge shape [110] → mixing 45 °
[110] → Spiral (the least preferred in terms of core energy)

  These various types and orientations of dislocations in the secondary layer are also shown in FIGS. FIG. 3 is a diagram showing a dislocation type propagating in a direction parallel to the growth direction in the (110) grown CVD synthetic diamond layer. The growth direction coincides with the <110> direction which is the vertical direction in the figure. Dislocations propagate from edged or 45 ° mixed dislocations in the primary CVD layer (the lower layer in each of the figures). FIG. 4 shows the dislocation type propagating through the (110) CVD synthetic diamond layer at an acute angle with respect to the growth direction. These dislocations propagate in the <100> direction at an angle of about 45 ° to the vertical direction. Again, dislocations propagate from the edge-like or 45 ° mixed dislocations in the primary CVD layer. Accordingly, FIG. 3 shows the dislocations occurring according to steps D and E as described above in connection with FIG. 2, whereas FIG. 4 illustrates the dislocations occurring according to step F as described above in connection with FIG. Show.

  In terms of energy, the most desirable dislocation (lowest core energy) in the secondary layer is the <110> mixed 60 ° dislocation. The <110> mixed 60 ° dislocation in the secondary layer is the result of the <100> mixed 45 ° dislocation in the primary layer or due to poor surface pretreatment of the (110) substrate formed from the primary layer. . Generally speaking, mixed dislocation types tend to be of lower energy than edge or spiral dislocations. The <100> mixed 45 ° dislocations in the primary layer occur due to growth on the substrate with poor pretreatment. Growing the primary layer with a good finish on a well-pretreated (001) substrate surface results in very little <100> mixed 45 ° dislocations in the primary layer and thus in the secondary layer It helps to minimize the number of <110> mixed 60 ° dislocations. Dislocations are also created at the interface between the secondary layer and the (110) substrate made from the primary layer. If the surface pretreatment of the (110) substrate is good, the dislocations that occur at the interface are only of the <100> blade or mixed 45 ° type. (110) If the surface pretreatment of the substrate is poor, <110> mixed 60 ° dislocations will be created further. Thus, minimizing the number of <110> mixed 60 ° dislocations in the secondary layer created at the interface can be achieved by processing the (110) substrate to high standards. If both of these steps were performed to eliminate <110> mixed 60 ° dislocations, <110> or <100> edged, <100> mixed 45 ° or <110> helical dislocations were grown, and Selected by adjustment of growth process parameters.

  In addition to the above, embodiments of the present invention provide (i) primary layer control to remove <100> mixed 45 ° dislocations to remove <110> mixed 60 ° dislocations in the secondary layer. And (ii) allows control of the surface pretreatment of the (110) substrate made from the primary layer to avoid the generation of <110> mixed 60 ° dislocations at the interface between the substrate and the secondary layer It is clear to do. In this case, the growth rate in the secondary layer may be controlled, and the resulting single crystal CVD synthetic diamond material is a non-parallel dislocation array comprising <100> mixed 45 ° and / or <100> edge dislocations. Will have.

In addition to controlling the orientation and type of dislocations that can be provided in a single crystal CVD synthetic diamond material by utilizing substrate surface treatment and controlling CVD growth parameters, it controls the density of dislocations formed in the material. It is also possible. In general, a lower concentration of defects at the growth surface of the substrate results in a lower density of defects in the CVD synthetic diamond material grown on the substrate. Further, careful control of CVD chemistry and process parameters such as pressure, substrate temperature, reactant flow rate and plasma temperature can reduce the density of defects grown in CVD synthetic diamond material. For example, the primary layer of (001) single crystal CVD synthetic diamond may have a dislocation density of 10 cm ⁻² to 1 × 10 ⁸ cm ⁻² . Further, the secondary layer of (110) single crystal CVD synthetic diamond should have a dislocation density of 10 cm ⁻² to 1 × 10 ⁸ cm ⁻² .

  Embodiments of the invention also examine single types of dislocations separately (eg, <110> 60 ° mixed dislocations or <100> 45 ° mixed dislocations), evaluate their basic characteristics, and device performance. It is possible to study which type of dislocations cause some loss in terms of Accordingly, embodiments of the present invention provide single crystal CVD synthetic diamonds in which the concentration, distribution, orientation and type of dislocations are selected and controlled to minimize these effects on material properties or even improve material properties. Open up the possibility of offering products. These material properties include optical birefringence, electrical (dielectric breakdown and μ), luminescence and mechanical (abrasion resistance and toughness).

Embodiments of the present invention are 10 cm ⁻² to 1 × 10 ⁸ cm ⁻² , 1 × 10 ² cm ⁻² to 1 × 10 ⁸ cm ⁻² or 1 × 10 ⁴ cm ⁻² to 1 × 10 ⁷ cm ^−2. A single crystal CVD synthetic diamond product with a significant volume having a dislocation density of can be provided. Alternatively or additionally, single crystal CVD synthetic diamond products can be 5 × 10 ⁴ or less, 5 × 10 ⁻⁵ or less, 1 × 10 ⁻⁵ or less, 5 × 10 ⁻⁶ or less, or 1 × 10 ⁻⁶ or less. It should have birefringence. The material may also contain a single substituted atomic nitrogen in a concentration range of 0.001 to 20 ppm, preferably 0.01 to 0.2 ppm.

  Although the description of the present invention primarily relates to {110} orientation growth, the inventors have also found that a similar description applies to CVD growth on {113} orientation substrates. In fact, the initial results show that there are several advantages of implementing the present invention on {113} oriented substrates. This is because the growth rate can be increased while still retaining the non-parallel dislocation array. It has been found that a thick, high quality single crystal CVD synthetic diamond material containing non-parallel dislocation arrays with {113} crystal orientation can be made. One significant difference between the {110} orientation and the {113} orientation is that for certain {110} embodiments, the non-parallel dislocation array is visible in the X-ray topographic cross-section, but not in luminescent conditions. In contrast, for certain {113} embodiments, non-parallel dislocation arrays are visible under luminescent conditions but not in X-ray topographic cross-sections. This is because dislocations in one particular line direction emit blue luminescent light (resulting in blue emission), while in other line directions, dislocations do not emit that way. For the {113} embodiment, the crystal line directions of the dislocations belonging to the non-parallel dislocation array are such that they do not emit blue luminescent light.

  Several examples of single crystal CVD synthetic diamond layers formed according to the methods described herein are shown in FIGS. 5-8, which are described below.

Example 1

A synthetic type 1bHPHT diamond plate with a pair of substantially parallel major faces within about 5 ° of the (001) orientation was selected. This plate was fabricated into a square substrate suitable for homoepitaxial synthesis of single crystal CVD synthetic diamond material by a process including the following steps.
i) laser cutting the substrate to produce a plate with all <100> edges, and ii) lapping and polishing the major surface where growth occurs. The lapped and polished part has a dimension of 400 μm thickness of approximately 6.0 mm × 6.0 mm with all faces {100}.

As disclosed in EP 1,292,726 and US 1,290,251, careful pretreatment of the substrate minimizes the level of defects at or below the substrate surface. It was. It is possible to reveal the level of defects introduced by this process by using plasma exposure etching. It is routinely possible to make a substrate whose defect density that can be measured after exposure etching depends mainly on the material quality and is less than 5 × 10 ³ mm ⁻² and usually less than 10 ² mm ⁻² . The surface roughness at this stage was less than 10 nm over a measurement area of at least 50 μm × 50 μm. The substrate was placed on a substrate carrier. The substrate and its carrier were then introduced into the CVD reactor chamber and the etch and growth cycle was initiated by feeding gas into the chamber as follows.

First, in-situ oxygen plasma etching using a pressure of 230 Torr 16/20/600 sccm (standard cubic centimeters per minute) O ₂ / Ar / H ₂ , a microwave frequency of 2.45 GHz and a substrate temperature of 780 ° C. Followed by a hydrogen etch to remove oxygen from the gas stream at this stage. The first stage growth process was then initiated by the addition of 22 sccm methane. Nitrogen was added to achieve a level of 800 ppb in the gas phase. Hydrogen was also present in the process gas. At this stage, the substrate temperature was 827 ° C. Over the next 24 hours, the methane content was increased to 32 sccm. These growth conditions were selected to give an α parameter value of 2.0 ± 0.2 based on previous tests, and these growth conditions were appellately confirmed by crystallographic examination. At the completion of the growth period, the substrate was removed from the reactor and the CVD synthetic diamond layer was removed from the substrate by laser sawing and mechanical polishing techniques.

  As a result of the study of the post-growth CVD synthetic diamond plate, the post-growth CVD synthetic diamond plate has no twins and cracks in the (001) plane, and the post-growth CVD synthetic diamond plate has The post-synthesis dimensions of the top (001) plane bounded by <110> sides and without twins were increased to 8.7 mm × 8.7 mm.

  The block is then processed using the same techniques (cutting, lapping, polishing and etching) as described above for the fabrication of the 1bHPHT plate to produce the major surface (110) and dimensions 3.8 × 3.2 mm. A plate with a well-pretreated surface with a thickness of 200 μm was produced. Next, during the synthesis stage, this was attached and grown using the same conditions as described above, except that the substrate temperature was 800 ° C. and nitrogen was not introduced as a dopant gas. This produced a CVD sample with a (110) major surface, and the CVD block had typical dimensions of 5.0 × 4.1 mm and a thickness of 1.6 mm.

  For this example, to study the dislocation structure, an X-ray cross-sectional topograph was recorded using the Bragg {533} reflection (corresponding to the (100) cross-section). An X-ray topograph is shown in FIG. FIG. 5 shows a single crystal CVD synthetic diamond layer grown on a vertically sliced (110) CVD synthetic substrate in accordance with an embodiment of the present invention including a parallel array of dislocations. As seen in this cross section, the dislocations form a parallel array that follows the growth direction, that is, the [110] direction. It can be said that this form corresponds to Step D or Step E shown in FIG.

  For the example shown in FIG. 5, the <110>: <001> growth rate ratio is 1.1, so growth may be dominated by kinetic factors rather than thermodynamic factors. Is within the “high” range. As is apparent from this image, the dislocations of Example 1 form a parallel array. It can be seen that 85% of the dislocations imaged by X-ray topography are in the 0 ° to 2 ° of the <110> growth direction.

Example 2

  A (110) substrate was made in the same manner as described in Example 1. The growth conditions for the second growth stage were the same as the growth conditions of Example 1 except that the substrate temperature was reduced by 70 ° C. to about 730 ° C. This produced a CVD sample with dimensions of 5.7 × 3.5 mm and a thickness of 1.4 mm. A small change in appearance with respect to the substrate temperature decreased the growth rate ratio <110>: <001> from a high value to a low value (about 0.4).

  For this example, to study the dislocation structure, an X-ray cross-sectional topograph was recorded using the Bragg {533} reflection (corresponding to the (100) cross-section). An X-ray topograph is shown in FIG. FIG. 6 shows a single crystal CVD synthetic diamond layer grown on a vertically sliced (110) CVD synthetic substrate in accordance with an embodiment of the present invention including a non-parallel array of dislocations. It can be easily understood that the dislocation forms a non-parallel array and propagates in a direction close to the [110] direction. It can be said that this form corresponds to Step F shown in FIG.

  For the example shown in FIG. 6, the <110>: <001> growth rate ratio is 0.4, so growth can be dominated by thermodynamic factors rather than kinematic factors. It is within the “low” range where the sex is likely. As can be seen from FIG. 6, the dislocation of Example 2 includes a non-parallel array. The dislocations form an array of intercrossing dislocations across the entire volume of the single crystal CVD synthetic diamond layer. The dislocation propagates in two directions, and the angle between the first direction and the second direction is 66 ° to 72 °. 95% of the dislocations present in the total volume of the sample are oriented between 9 ° and 12 ° in the <100> line direction. Furthermore, 95% of the dislocations present in the total volume of the sample are 33 ° to 36 ° from the <110> growth direction. According to the analysis result of 12 NV centers, all of these NV centers were grown in a state where the preferential orientation was in the <111> direction out of the plane with respect to the (110) growth plane.

  FIG. 7 is a diagram showing a birefringence photomicrograph of the CVD synthetic diamond material of FIG. 6, showing a relatively small strain in view of the large dislocation density for this sample. Further, according to the initial data, the CVD synthetic diamond material shown in FIGS. 6 and 7 has increased material hardness. An initial review paper by Ballmer et al., "J. Phys .: Condensed Matter", 2009, Vol. 21, 364221 has already been (110). It discloses that tools made with orientations have less wear and impact resistance than tools with a (001) plane. According to the initial data of the new material described herein, the new material has the advantage of (110) diamond in terms of wear resistance and increased hardness (eg at least 100 GPa, more preferably at least 120GPa) in combination.

Example 3

  Synthetic type 1bHPHT diamond was cut to form a plate with a pair of substantially parallel major faces within a range of about 5 ° of (113) orientation. The major surface on which the growth takes place was further processed by lapping and polishing.

  The substrate was placed on a substrate carrier. The substrate and its carrier were then introduced into the CVD reactor chamber. Etching and growth cycles were performed as described in Example 1, except that the substrate temperature was reduced by 70 ° C. to about 730 ° C. as described in Example 2.

  The resulting single crystal CVD synthetic diamond material can be seen under luminescent conditions (emitting blue luminescent light properties of dislocations in certain crystal line directions), but non-parallel not visible in X-ray topographic cross-sections It was found to contain a dislocation array.

  FIG. 8 shows a single crystal grown on a {110} and {113} oriented substrate (explained in Example 2 and Example 3) under X-ray topography cross section (upper) and luminescent conditions (lower). A CVD synthetic diamond layer is shown. As can be seen in the figure, for the {110} embodiment, the non-parallel dislocation array is visible in the X-ray topographic cross-sectional image but not in the luminescent image, whereas for the {113} embodiment, the non-parallel dislocation array. Is visible in the luminescent image but not in the X-ray topographic cross-sectional image.

  While the invention has been particularly shown and described with respect to preferred embodiments, those skilled in the art will recognize that various changes in form and detail may be made without departing from the scope of the invention as set forth in the claims. Let's do it.

Claims (12)

  A single crystal CVD synthetic diamond layer having a non-parallel dislocation array, the non-parallel dislocation array comprising a plurality of dislocations forming an array of cross-cross dislocations when viewed under X-ray topographic cross-sectional or luminescent conditions; The thickness of the single crystal CVD synthetic diamond layer is 1 μm or more, the non-parallel dislocation array occupies at least 30% of the total volume of the single crystal CVD synthetic diamond layer, and the direction in which the dislocation propagates is A single crystal CVD synthetic diamond layer, measured in the average direction over at least 30% of the total length. The thickness of the single crystal CVD synthetic diamond layer is 10μm or more, claim 1 single crystal CVD synthetic diamond layer according. The single crystal CVD synthetic diamond layer according to claim 1 or 2, having a dislocation density of 10 cm ^-2 to 1 x 10 ⁸ cm ^-2 . The single crystal CVD synthetic diamond layer according to claim 1, which has a birefringence of 5 × 10 ⁴ or less.   The single crystal CVD synthetic diamond layer according to any one of claims 1 to 4, wherein the single crystal CVD synthetic diamond layer is a {110} or {113} oriented layer. The single crystal CVD synthetic diamond layer according to any one of claims 1 to 5, wherein the non-parallel dislocation array extends over a volume that occupies at least 40% of the total volume of the single crystal CVD synthetic diamond layer. The non-parallel dislocation array has a first set of dislocations propagating in a first direction through the single crystal CVD synthetic diamond layer and a second propagating in a second direction through the single crystal CVD synthetic diamond layer. It includes dislocations forming a second set, the angle of the first direction and the second direction is 40 ° to 100 ° as viewed in the X-ray topography sectional view or luminescent conditions claims 1-6 A single crystal CVD synthetic diamond layer according to any one of the above. Direction dislocations propagated is measured expressed as mean direction over a significant length of the dislocation, the significant length is at / or at least 50μm with at least 40% of the total length of the dislocation, claims 1-7 A single crystal CVD synthetic diamond layer according to any one of the above. The non-parallel dislocation array is visible in X-ray topography but not visible under luminescent conditions, or alternatively, the non-parallel dislocation array is visible under luminescent conditions but not in X-ray topography. The single crystal CVD synthetic diamond layer according to any one of claims 1 to 8 . The single crystal CVD synthetic diamond layer according to any one of claims 1 to 9 , having a hardness of at least 100 GPa. 11. A single crystal CVD synthetic diamond object comprising the single crystal diamond layer according to any one of claims 1 to 10 , wherein the single crystal diamond layer is at least 30% of the total volume of the single crystal CVD synthetic diamond object. the occupied, single crystal CVD synthetic diamond object. The single crystal CVD synthetic diamond object of claim 11 , wherein the single crystal CVD synthetic diamond object is cut into a jewel form.

Images